You can configure the days when you want to get daily check-ins from the team members (as manager), or when you want to be filling the reports (as user).
There are two considerations:
As admin, you can define whether you want each user to be able to configure the days they work (aka. get the daily reminders to fill the reports)
You must go the Check-ins settings and enable the feature "Allow team members to specify their own working days" and then every user will be able to define it.
As Admin, you can just force the working days for all the users
In this case, you should disable the feature "Allow users to specify their own working days?", and then select the days of work you want to apply to all the organization members.